1. Field of the Invention
The present invention relates to a data communicating apparatus for communicating data between first and second devices which are contactlessly closely arranged or which approach each other by using an induction electromagnetic field and to an oscillator which is used in the communicating apparatus and transmits data by intermittently oscillating.
2. Prior Art Statement
Hitherto, for instance, as shown in JP-A-62-63050, there has been proposed a data transmitting apparatus in which a data storing device to store tool data is provided for a tool shank or the like of a machine tool, the data is serially transmitted and written from a data input/output apparatus into the data storing device, or the content written is read out. In such a data transmitting apparatus, the data communication between the data input/output apparatus and the data storing device is performed by using predetermined high frequency signals by frequency shift keying (FSK) modulating those high frequency signals.
However, according to the conventional data transmitting apparatus, each of the data storing device and data input/output apparatus needs a PLL circuit or the like to demodulate the FSK signal, so that a large electric power consumption is required. There is a case where an AC voltage induced from the data input/output (I/O) apparatus is rectified and the data storing device uses the resultant rectified voltage as a power source. In such a case, if the electric power consumption is large, data communication cannot be performed unless the induced voltage is high, so that there is a drawback in that a distance at which the data communication can be performed is short. On the other hand, when the data storing device has a battery, there is a drawback in that the life of the battery is short. The applicant of the present invention has already proposed a system in Japanese Patent application 62-52692 in which in order to reduce the electric power consumption of the data storing device, when data is transmitted from the data storing device to the data I/O apparatus, a resonance frequency of a resonance circuit is discontinuously changed on the basis of the transmission data. In such a case, although the electric power consumption of the data storing device can be reduced, since a communication range is determined by a coupling coefficient between the data storing device and the data I/O apparatus, there is a drawback in that even if an output from the data I/O apparatus is enlarged, the communication distance cannot be increased.
On the other hand, as shown in FIG. 16, there has been known a Colpits oscillator which is an LC type oscillator for transmitting a signal by the electromagnetic induction by intermittent oscillation. In the diagram, a collector of a transistor Tr.sub.1 is connected to one end of an LC resonance circuit 51 consisting of a coil L.sub.1 and capacitors C.sub.21 and C.sub.22. A feedback resistor R.sub.21 is connected between a middle point of the coils C.sub.21 and C.sub.22 and an emitter of the transistor Tr.sub.1. The emitter of the transistor Tr.sub.1 is connected to the ground through an emitter resistor R.sub.22. A predetermined DC voltage is applied to one end of the resonance circuit 51. A middle point of resistors R.sub.23 and R.sub.24 to divide the power source voltage is connected to the base of the transistor Tr.sub.1. A predetermined voltage is applied as a bias to the base of the Tr.sub.1 and the base is connected to the ground by a capacitor C.sub.23 in an AC manner. An FET 52 for switching is provided to intermittently apply and shut off the terminal voltage of the base of the Tr.sub.1. The FET 52 is intermittently turned on/off in accordance with an input signal and the base of the oscillating transistor Tr.sub.1 is connected to the ground or a predetermined bias voltage is applied thereto. Thus, as shown in FIGS. 17a and 17b, the oscillation can be intermittently performed in correspondence to the input voltage which is applied to the FET 52.
However, in such an oscillator, since the base voltage of the oscillating transistor is controlled and the oscillation is started and stopped, the leading time of the oscillation is slow and the trailing time thereof is also slow, so that even if the supply of the input signal is stopped, the attenuating vibration remains and the amplitude gradually decreases. Thus, there is a drawback such that the oscillation cannot be intermittently performed at a high speed and a data transmission speed cannot be set to a high speed.